The present invention relates to the image forming apparatus incorporating a fixing unit, which is includes either a fixing belt or a fixing roller, and effectively used in the image forming apparatus of an electrophotographic copier and printer, and particularly to the fixing unit and image forming apparatus improved to ensure a uniform distribution of the temperature on the surface of the fixing belt or the fixing roller for heating a toner image.
A belt type fixing unit known so far includes the one comprising (1) a backup/heating roller containing a heating means made up of a halogen lamp, (2) a fixing belt applied to two backup rollers consisting of backup/pressure rollers, and (3) a pressure roller which rotates by giving pressure through the aforementioned backup/pressure roller and fixing belt; wherein a toner image is fixed onto the paper with unfixed toner image by the pressure of the pressure roller and heating of the fixing belt.
Such a fixing unit is arranged in such a way that; a temperature sensor as a means of detecting temperature is provided close to or in contact with the external surface of the backup/heating roller on the center in the longitudinal direction, for example, and the output information of the temperature sensor is used to control the power supply to the heating means by a control means, thereby allowing the temperature on the fixing belt surface to be maintained within the range of temperature suited to fixing of toner image.
The above fixing unit is mounted on a wide range of image forming apparatuss for ease of handling. One of the problems with the aforementioned fixing unit, however, is how to reduce the warming up time. Many proposals have been made during the course of a long period of time. One of such proposals is to decrease heat capacity by reducing the thickness of an endless fixing belt.
This is to reduce the thickness of the metallic substrate at the center constituting the fixing belt and the rubber on the outside layer, thereby ensuring the temperature on the fixing belt surface to reach the toner fixing temperature earlier.
It has been found out, however, that another issue occurs even if the thickness of the fixing belt can be reduced to ensure a specified mechanical strength to be maintained, and even if it is possible to reduce the time until stable fixing of the fixing belt surface is ensured after electric power is supplied to the heating means.
For example, when continuous fixing is performing using a small-sized paper with a toner image formed which is fed at the center with reference to the fixing belt, heat on the surface of the fixing belt corresponding to the aforementioned small-sized paper feed area is consumed to heat the paper. However, heat on the surface of the aforementioned fixing belt corresponding to the non-paper feed area on the right and left sides is not consumed. Moreover, heat is stored in the non-paper feed area due to a small shift of heat along the direction of the width of the fixing belt.
Further, electric power is supplied to the heating means to ensure that the temperature on the fixing belt surface in the paper feed area deprived of heat can be kept at a specified fusible temperature. This will increase the amount of heat stored in the portion of the fixing belt corresponding to the aforementioned non-paper feed area, with the result that the temperature range suited for fixing is much exceeded.
When large-sized paper utilizing the non-paper feed area on the right and left sides of the fixing belt is used at the time of the excessive temperature rise mentioned above, and the toner image formed on this paper must be fixed, then irregularity of gloss or high temperature offset occurs to the surface of the paper in conformity to irregular forms of the paper and toner layer caused by the difference of the temperatures heretofore between paper feed area and non-paper feed area. This will reduce the service life of the rubber layer of the fixing belt.
Suck a problem is caused by the aforementioned fixing belt which is made into a substance of low heat capacity through the reduction of the thickness of the fixing belt, with the result that there is a reduction in the function of shifting the heat stored in the non-paper feed area to a place of lower temperature.
Another example of the known image forming apparatus is the one provided with a fixing unit arranged in such a way that paper carrying a toner image is fed between the fixing belt rotatably supported by the backup roller and heated by a proper heating source, and a roller which rotates in contact with this fixing belt, and the aforementioned toner image is fixed to this paper by the pressure and heat produced between the two.
One form of the aforementioned fixing unit conceivable is the one where a heating source consisting of a halogen lamp is installed inside the loop formed by a fixing belt to heat the fixing belt directly, thereby reducing the warming up time.
Such a system, however, is accompanied by the following problem: During the standby period subsequent to the temperature of the fixing belt having been raised to the value which permits fixing, the temperature of the aforementioned fixing belt must be kept at the value allowing fixing or at a proper value lower than the fusible temperature with consideration given to energy saving. This requires the fixing belt to be rotated in order to maintain the temperature of the entire fixing belt, because the heat source is arranged opposite to part of the fixing belt. Further, a greater amount of heat is discharged due to a greater size of the fixing belt, with the result that energy efficiency is poor in such a conventional system.
Further, when paper of a smaller size with respect to the width for fixing and heating on the fixing belt is subjected to continuous fixing in the fixing process for example, there is an excessive rise of temperature in the non-paper feed area (e.g. the portion formed on the right and left sides of the fixing belt which does not contribute to fixing). If large-sized paper is subjected to fixing under this condition, irregular fixing occurs on paper in such a conventional system.
In other words, when the image forming apparatus is assumed to be arranged with reference to the center in such a way that there is an agreement between the center of the fixing belt along the direction of the width and that of the paper to be fixed, for example, the temperature sensor is installed close to or in contact with the center of the fixing belt along the direction of the width. Power supply to the heat source is controlled based on the information detected by this temperature sensor.
Accordingly, the fixing belt of the paper feed area in contact with the small-sized paper is always maintained at a fusible temperature, but the heat of the non-paper feed area is hardly used. Moreover, excessive amount of heat is stored because the heat is replenished by turning on the heat source for keeping the temperature in the paper feed area. This gives rise to the aforementioned problem.
This problem is caused by poor heat transfer capacity along the direction of the width as a result of reducing the heat capacity of the fixing belt.
In a fixing unit used in an image forming apparatus such as a copier, printer and facsimile machine characterized by a high level of technological perfection and high stability, a heating roller fixing method using a rubber roller as a fixing heating roller is employed over an extensive scope ranging from low speed to high speed machines and from monochrome to full-color machines.
In the fixing unit according to the conventional heating roller fixing method, however, a heating roller for fixing with a high heat capacity must be heated when the transfer material or toner is heated, and this is disadvantageous in energy saving. Moreover, this requires much time in warming the fixing unit at the time of printing (longer warming up time).
To solve this problem, a fixing unit according to film fixing method has been proposed and has come into use in recent years. This fixing unit is characterized by; (1) a substantial improvement in heat conductivity realized by the heat capacity reduced by use of a film (thermal fixing film) which allows the heating roller to be made into a thermal fixing film having the ultimate thickness, and (2) a quick start method which saves energy and which hardly requires warming up time, this quick start method being realized by direct contact of a temperature-controlled heat-generating body (ceramic heater) and inductive heat generating body to the thermal fixing film.
Further, Japanese Patent Laid-Open NO. Sho52-106741, Japanese Patent Laid-Open NO. Sho57-82240, Japanese Patent Laid-Open NO. Sho57-102736 and Japanese Patent Laid-Open NO. Sho57-102741 disclose a fixing method characterized by quick start without requiring warming up time, wherein a substrate (transparent base body) is used as a heat fixing roller (fixing roller member) which is a variation of the heating roller, and the heat from the halogen lamp (heating means) installed inside is irradiated to toner, whereby heating and fixing are performed. Further, Japanese Patent Laid-Open NO. Sho59-65867 discloses a fixing method wherein a fixing roller is configured with a light absorbing layer provided on the outer surface of the substrate (transparent base body), and light from a halogen lamp (heating means) installed inside the cylindrical transparent base body is absorbed by the light absorbing layer provided on the outer surface of the transparent base body, whereby a toner image is fixed by the heat of the light absorbing layer.
Both the fixing units disclosed in the Japanese Patent Laid-Open NO. Sho52-106741 and the Japanese Patent Laid-Open NO. Sho59-65867 are intended to realize energy saving and quick start based on reduced warming up time. In the former fixing unit, the light from the halogen lamp (heating means) is irradiated through the substrate (transparent base body) to heat and fix the toner. In the latter fixing unit, a fixing roller is arranged by providing a light absorbing layer on the outer surface of the substrate (transparent base body) and light from the halogen lamp is applied to the absorbing layer through the transparent base body and the toner is fixed by the heat of this absorbing layer. However, fixing performances are poor. To solve this problem, the present inventors proposed in the Japanese Patent Laid-Open NO. Hei11-327341 a fixing unit and an image forming apparatus using this fixing unit characterized by quick start (high-speed eating) and excellent fixing capability, wherein a halogen lamp (heating means) is used, and elastic layer (translucent elastic layer) consisting of a rubber layer is provided between the transparent base body and light absorbing layer to form a fixing roller made of a soft roller, thus allowing the absorbing layer to be heated by the light from the halogen lamp (heating means).
In the fixing roller member of the fixing unit used in the aforementioned image forming apparatus, a glass member is mainly used as a transparent base body. The fixing roller member using the glass member (glass core) as a transparent base body enables short-time preheating, but it is characterized by lower than the one using the metallic member (metallic core). So when a transfer material (recording paper) with the width smaller than the heating width of the heating means (halogen lamp) is passed, earlier deterioration of the fixing roller member will be caused by an excessive rise of temperature at the end portion. To solve this problem, a temperature-equalizing roller in contact with the fixing roller member is used in order to shift (disperse) the heat on the surface of the fixing roller member. However, this has the problem of prolonged preheating time in the fixing unit. At the time of continuous passing of transfer materials of small width, it is not effective in reducing the temperature rise on the end portion of the fixing roller, due to lack of uniformity in the widths of the nip portions (equalization roller nip portions) between the fixing roller member and temperature-equalizing roller, or due to ineffective heat dispersion of the fixing roller member by the temperature-equalizing roller. This results in earlier deterioration of the fixing roller member. It is also difficult to avoid an increase in the size of the fixing unit of complicated structure used for formation of color image.
Also known is an image fixing unit arranged in such a way that the recording paper (hereinafter referred to as xe2x80x9cpaperxe2x80x9d) carrying an toner image is led to the image fixing unit called a heating roller type fixing unit, and is made to pass between a rotable fixing roller with a built-in heat source and a nip roller which rotates pressing against this fixing roller; wherein the aforementioned toner image is fixed on the paper by the pressure and heat provided by these two rollers.
Also known is the art of temperature control, which ensures the temperature on the surface of the fixing roller to be kept within the range of a specified temperature in the aforementioned image fixing unit.
The aforementioned image fixing unit is very useful because of easy handling, compact configuration and excellent safety, and is built in a great variety of image forming apparatus. It is now put into effective use.
However, when the core of the fixing roller is made, for example, of glass, and arrangements are made to enable quick warming up, the following problems occur:
Namely, when the paper having a width smaller than heating width has to be treated on a continuous basis, the roller containing the aforementioned roller core has a lower heat conductivity than the roller with a metallic core. So even if effective fixing of paper is possible, temperature in the area outside the contact area with paper, namely, the temperature on both ends of the heating width on the fixing roller becomes excessive. If wide paper is treated under this condition, irregular gloss will be produced on the paper corresponding to the boundary area of temperature. To prevent temperature rise on the end portion, an art of installing a cooling fan is also proposed, but thermal efficiency is poor.
To overcome the abovementioned drawbacks in conventional image-forming apparatus and fixing units, objects of the present invention will be described in the following.
The first object of the present invention is to provide a fixing unit characterized by reducing the rise of temperature in the non-paper passing area of the fixing belt whose wall thickness is reduced for decreased heat capacity and by ensuring a uniform temperature distribution on the surface of the fixing belt suited to fixing of toner image on paper, thereby solving the problem of irregular gloss or high temperature offset.
The second object of the present invention is to provide (1) a fixing unit characterized by shorter warming up time without the need of rotating the fixing roller even in the state of waiting for fixing, and (2) an image forming apparatus which enables a quick re-rise of temperature when the waiting mode is switched over to the fixing mode.
The third object of the present invention is to provide an image forming apparatus designed in a simple structure which ensures effective heat transfer in the paper passing area and non-paper passing area on the fixing belt and enables a uniform temperature to be maintained on the surface of the fixing belt.
The fourth object of the present invention is to provide an image forming apparatus designed in a simple structure characterized by (1) reducing the rise of temperature at the end portion of the roller member at the time of continuous passing of the transfer material of small width, without affecting the preheating time of the fixing unit, (2) enabling quick startup, and (3) incorporating a fixing unit the optimum to color image formation.
The fifth object of the present invention is to provide an image forming apparatus designed in a simple structure capable of reducing the excessive rise of temperature on both ends on the fixing roller even in the process of continuous passing of paper having a width smaller than heating width on the fixing roller.
Accordingly, to overcome the cited shortcomings, the abovementioned objects of the present invention can be attained by fixing units and image-forming apparatus described as follow.
(1) A fixing unit, comprising: a fixing belt threaded on a plurality of supporting rollers; and a temperature-equalizing member to equalize a temperature distribution of the fixing belt in its width direction; wherein the temperature-equalizing member moves from a separate position to a first pressure-contacting position at which the temperature-equalizing member pressure-contacts the fixing belt, and further moves to a second pressure-contacting position while maintaining a pressure-contacting state with the fixing belt; and wherein a contact area of the temperature-equalizing member and the fixing belt is enlarged at the second pressure-contacting position, compared to that at the first pressure-contacting position, and the temperature-equalizing member can park at either the first pressure-contacting position or the second pressure-contacting position.
(2) The fixing unit of item 1, wherein the temperature-equalizing member is pressed onto a supporting roller, serving as one of the supporting rollers, with the fixing belt between them, and moves along an outer shape of the supporting roller.
(3) The fixing unit of item 1, wherein the temperature-equalizing member is a metallic roller.
(4) The fixing unit of item 3, wherein the metallic roller comprises: a release layer having a thickness in a range of 10-100 xcexcm and provided on an outer surface of the metallic roller.
(5) The fixing unit of item 1, wherein the temperature-equalizing member moves from the first pressure-contacting position to the second pressure-contacting position either continuously or step by step.
(6) An image-forming apparatus having a function of fixing a toner image onto a sheet, comprising: a fixing belt threaded on at least two of supporting rollers; and a temperature-equalizing member equipped in a vicinity of a supporting roller, serving as one of the supporting rollers, to equalize a temperature distribution of the fixing belt in its width direction; a sheet-size detecting section to detect a size of the sheet currently selected; a temperature detecting section to detect a temperature of the temperature-equalizing member; and a controlling section to control a moving action of the temperature-equalizing member so that, when the sheet-size detecting section detects that the size of the sheet is small, the temperature-equalizing member pressure-contacts the fixing belt at a first contacting position, and to change a contact angle of the fixing belt, when the temperature detecting section detects that the temperature of the temperature-equalizing member exceeds a reference value.
(7) The image-forming apparatus of item 6, wherein, when the temperature of the temperature-equalizing member, positioned at the first contacting position, exceeds the reference value, the controlling section controls the moving action of the temperature-equalizing member so that the temperature-equalizing member moves along an outer shape of the supporting roller to a second contacting position, while being pressed onto the supporting roller with the fixing belt between them.
(8) An image-forming apparatus having a function of fixing a toner image onto a sheet, comprising: a fixing belt threaded in a shape of a loop; a heat source to heat the fixing belt up to a fixable temperature, which makes a fixing operation possible; and a temperature-equalizing member, disposed in an interior of the loop, to equalize a temperature distribution of the fixing belt in its width direction; wherein the temperature-equalizing member moves between a release position at which the temperature-equalizing member does not contact the fixing belt and a pressure-contacting position at which the temperature-equalizing member pressure-contacts the fixing belt.
(9) The image-forming apparatus of item 8, further comprising: a sheet-size detecting section to detect a size of the sheet currently selected; wherein, when the sheet-size detecting section detects that the size of the sheet is smaller than a fixable width of the fixing belt, the temperature-equalizing member pressure-contacts the fixing belt at the pressure-contacting position.
(10) The image-forming apparatus of item 8, wherein a base of the fixing belt is made of a metallic material.
(11) The image-forming apparatus of item 8, wherein the temperature-equalizing member is made of aluminum.
(12) The image-forming apparatus of item 9, wherein, when the sheet-size detecting section detects that the size of the sheet is a predetermined small size, and detects that a large number of sheets, which exceeds a predetermined number of sheets, are continuously processed in the fixing operation, the temperature-equalizing member pressure-contacts the fixing belt at the pressure-contacting position.
(13) An image-forming apparatus having a function of fixing a toner image onto a sheet, comprising: a fixing roller, including a heater and a base body on which an elastic layer is formed; and a temperature-equalizing roller to equalize a temperature distribution of the fixing roller in its width direction; wherein the temperature-equalizing member can pressure-contact the fixing roller with a pressure-contacting force, and can be released from a pressure-contacting state; and wherein a value of the pressure-contacting force is selectable in a plurality of step values.
(14) An image-forming apparatus having a function of fixing a toner image onto a sheet, comprising: a fixing roller, including a heater and a base body on which an elastic layer is formed; and a temperature-equalizing roller unit to equalize a temperature distribution of the fixing roller in its width direction; wherein the temperature-equalizing roller unit includes a temperature-equalizing roller and a shaft, serving as a rotating axis of the temperature-equalizing roller; and wherein the temperature-equalizing roller is movable in a longitudinal direction of the shaft.
(15) The image-forming apparatus of item 14, wherein the temperature-equalizing roller is movably coupled to the shaft by engaging female and male screws formed on the temperature-equalizing roller and the shaft respectively.
(16) The image-forming apparatus of item 14, wherein a rotating velocity of the shaft is variable.
(17) The image-forming apparatus of item 15, wherein two temperature-equalizing rollers are movably coupled to the shaft, and a winding direction of the female screw formed on one of the two temperature-equalizing rollers is opposite to that formed on the other one.
(18) The image-forming apparatus of item 17, wherein a total length of the two temperature-equalizing rollers is substantially equal to a maximum width of the sheet.
(19) An image-forming apparatus having a function of fixing a toner image onto a sheet, comprising: a fixing roller, including a heater and a base body on which an elastic layer is formed; and a temperature-equalizing roller unit to equalize a temperature distribution of the fixing roller in its width direction; wherein the temperature-equalizing roller unit includes two temperature-equalizing rollers, a shaft serving as a rotating axis of the two temperature-equalizing rollers and a phase deviation preventive member to fix a mutual phase relationship between the two temperature-equalizing rollers in respect to the shaft; and wherein the two temperature-equalizing rollers are movable in a longitudinal direction of the shaft.
(20) The image-forming apparatus of item 19, wherein the phase deviation preventive member is insertably and drawably engaged into the two temperature-equalizing rollers.
(21) The image-forming apparatus of item 19, wherein a total length of the two temperature-equalizing rollers is substantially equal to a maximum width of the sheet.
(22) The image-forming apparatus of item 13, wherein the fixing roller comprises a transparent base body.
(23) The image-forming apparatus of item 13, wherein a diameter of the temperature-equalizing roller gradually decreases according as a position of the diameter approaches an end of the temperature-equalizing roller, so that the temperature-equalizing roller partially contacts the fixing roller.
(24) An image-forming apparatus having a function of fixing a toner image onto a sheet, comprising: a fixing roller, including a heater and a base body on which an elastic layer is formed; and a plurality of temperature-equalizing roller units to equalize a temperature distribution of the fixing roller in its width direction; wherein each of the temperature-equalizing roller units contacts the fixing roller at each of areas being different relative to each other.
(25) The image-forming apparatus of item 24, wherein the temperature-equalizing roller units pressure-contact the fixing roller in a plurality of pressure-contacting modes.
(26) The image-forming apparatus of item 25, wherein one of the pressure-contacting modes is selected corresponding to temperatures of temperature-equalizing rollers mounted on the temperature-equalizing roller units, or a width of the sheet, or combination of the temperatures of the temperature-equalizing rollers and the width of the sheet.
(27) The image-forming apparatus of item 25, wherein the temperature-equalizing roller units contact a non-contacting roller, which is not in contact with the fixing roller.
(28) The image-forming apparatus of item 27, wherein a surface of the non-contacting roller is coated with an elastic material.
(29) The image-forming apparatus of item 24, wherein the temperature-equalizing roller units are disposed at adjacent positions, so that the temperature-equalizing roller units contact each other.
(30) The image-forming apparatus of item 29, wherein a number of the temperature-equalizing roller units is an even number.
(31) The image-forming apparatus of item 30, wherein surfaces of temperature-equalizing rollers, mounted on at least a half number of the temperature-equalizing roller units, are coated with an elastic material.
(32) The image-forming apparatus of item 24, wherein the fixing roller comprises a transparent base body.
(33) The image-forming apparatus of item 24, wherein one of the temperature-equalizing roller units comprises a temperature-equalizing roller, and a diameter of the temperature-equalizing roller gradually decreases according as a position of the diameter approaches an end of the temperature-equalizing roller, so that the temperature-equalizing roller partially contacts the fixing roller.
(34) A fixing unit, comprising: a fixing roller; and a temperature-equalizing roller to equalize a temperature distribution of the fixing roller in its width direction; wherein the temperature-equalizing member can pressure-contact the fixing roller, and can be released from a pressure-contacting state; and wherein an angle, at which a rotating axis of the temperature-equalizing roller is inclined to that of the fixing roller, is changeable.
(35) The fixing unit of item 34, wherein the angle can be controlled in response to a width of a sheet being under a fixing operation.
(36) The fixing unit of item 34, wherein the angle can be controlled in response to a temperature of the temperature-equalizing roller.
(37) The fixing unit of item 34, wherein the fixing roller comprises a transparent base body and a transparent elastic layer.
Further, to overcome the abovementioned problems, other fixing units and image-forming apparatus, embodied in the present invention, will be described as follow:
(38) A fixing unit characterized by comprising a temperature-equalizing member which is fixed and held at the first position in contact with the aforementioned fixing belt by being displaced from a separate position along the direction of the width of the fixing belt applied on multiple backup rollers, serving as supporting rollers, and at the second pressed position where contact area with the aforementioned fixing belt is expanded by being displaced while the pressed position is maintained.
(39) An image forming apparatus characterized by comprising: a fixing belt applied to at least two backup rollers; a temperature-equalizing member installed in the vicinity of one of the aforementioned backup roller; a detecting means for detecting the size of the paper to be used on a selective basis; a control means for ensuring that the temperature-equalizing member is pressed against the first pressed position when the aforementioned detecting means has sensed that the paper is small-sized; a detecting means for detecting the temperature of the aforementioned temperature-equalizing member; and a control means which allows the aforementioned temperature-equalizing member to be moved in such a way that the contact angle with respect to the fixing belt is changed when the temperature of the temperature-equalizing member has exceeded the reference value.
(40) An image forming apparatus characterized in that a heat source is incorporated in at least of the pressing means installed to ensure that the fixing belt and paper can be held in the pressed state, and a heat source is installed for direct heating of the aforementioned belt.
(41) An image forming apparatus characterized in that a heat source is incorporated in at least of the pressing means installed to ensure that the fixing belt and paper can be held in the pressed state, and a heat source is incorporated in at least one of multiple backup rollers for supporting the aforementioned fixing belt.
(42) An image forming apparatus comprising an image forming apparatus described in (40) or (41) wherein control is made to ensure that the temperature of only the pressing means incorporating a heat source is maintained at the specified value by a control means in the standby state subsequent to the arrival of said fixing belt temperature to the fusible temperature.
(43) An image forming apparatus characterized in that a temperature-equalizing roller is provided in the loop of the rotatable fixing belt supported in a loop form where temperature is raised to the fusible temperature by a heat source in such a way that the temperature-equalizing roller can be pressed against the fixing belt and pressing can be released.
(44) An image forming apparatus comprising a fixing unit further comprising a heating means and a fixing roller member having an elastic layer on the substrate, wherein the aforementioned fixing roller member is provided with a temperature-equalizing roller in such a way that the temperature-equalizing roller can be pressed against the fixing belt and that the pressing can be released, and the contact pressure between the temperature-equalizing roller and the fixing roller member can be selected from multiple values.
(45) An image forming apparatus comprising a fixing unit further comprising a heating means and a fixing roller member having an elastic layer on the substrate, wherein the aforementioned fixing roller member is provided with a temperature-equalizing roller for ensuring uniform temperature of the fixing roller member, and the aforementioned temperature-equalizing unit member comprises a temperature-equalizing roller rotary shaft and a temperature-equalizing roller which is movable on the temperature-equalizing roller rotary shaft.
(46) An image forming apparatus comprising a fixing unit further comprising a heating means and a fixing roller member having an elastic layer on the substrate, wherein the aforementioned fixing roller member is provided with a temperature-equalizing roller for ensuring uniform temperature of the fixing roller member, and the aforementioned temperature-equalizing unit member comprises a temperature-equalizing roller rotary shaft and two temperature-equalizing rollers which are movable on the temperature-equalizing roller rotary shaft; the aforementioned image forming apparatus further characterized in that these two temperature-equalizing rollers have a phase deviation preventive member for fixing the mutual phase around the temperature-equalizing roller rotary shaft.
(47) An image forming apparatus comprising a fixing unit further comprising a heating means and a fixing roller member having an elastic layer on the substrate; the aforementioned image forming apparatus further characterized by comprising multiple temperature-equalizing roller units in contact with the aforementioned roller member in different areas.
(48) An image forming apparatus comprising a temperature-equalizing roller arranged in such a way that it can be pressed against a fixing roller and that the pressing can be released, wherein an angle formed between the shaft of the temperature-equalizing roller and that of the fixing roller can be changed.